Two models of lung growth are being used to evaluate the control of connective tissue accumulation as related to normal alveolar structure. In normal neonatal lung growth in the rabbit, glycosaminoglycan content, types and synthesis have been quantitated. The changes seen with lung growth may have signficant influence on the mechanical properties of lung during these periods. In post-pneumonectomy lung growth in the rabbit, the total number of alveoli doubles and alveolar structure appears normal. This data, together with prior informatin on the control of collagen synthesis in this model, suggest there are complex controls which may be harnessed to induce alveolar regeneration.